The extensive commercial potential of carbon residue materials including graphene, graphene oxide, graphite and graphite oxide is well documented owing to their exceptional electrical, thermal, chemical and mechanical properties. These materials have found application in areas as diverse as composite materials, energy storage and conversion, sensors, drug delivery, field emission devices and nano-scale electronic components and their uses include liquid and gas filtration, gas storage, energy storage, electronics, coatings, and medical applications.
Graphene oxide can be produced from graphite oxide by chemical processes including Hummers method or the dispersion of graphite oxide into basic solution. Functionalization of graphene and graphene oxide flakes is widely studied.
Graphene-based materials have been studied for over four decades, including the transport properties in exfoliated graphene oxide layers, graphene grown on silicon carbide and copper substrates. A variety of studies involve the use of chemically modified graphene (CMG) to make new materials. Of the available strategies, exfoliation to form graphene oxide layers has been favoured in the mass production of graphene oxide, but faces the challenge of producing exfoliated graphene oxide with a controlled thickness, and the dimensions of the individual thin films or flakes is typically limited to few 10s to 100s of square microns in area dimension. Production of large area graphene via chemical vapour deposition has led to high quality graphene oxide but the flakes are still limited in area and production is challenging to scale up for thin films or flakes over a few millimetres2 in area.
Graphene production methods include the micromechanical cleavage, epitaxial growth, and chemical synthesis involving oxidation-intercalation and exfoliation-reduction of graphite. The chemical synthesis route from graphite via reduction of graphene oxide has been reported to achieve a single or a few layers of graphene at large-scale.
Many applications of carbon residue materials require their production as continuous sheets or flakes which have a thickness of less than 20 nm and an area divided by thickness ration (A/T) greater than 1010 nanometres (nm), and their assembly into three-dimensional structures. As suggested above, it remains challenging to economically mass produce flakes or sheets of graphene-based materials of useful size and thickness.
The present invention was devised with the foregoing in mind.